Debugging.

Since MPICH is portable, it has no built-in debugging support. For some devices, it is possible to start the root process under a debugger, or to start the entire application under a parallel debugger. The best debugging option for MPICH is the Totalview debugger [8], a commercial product from Dolphin Interconnect Solutions that is one of the best parallel debuggers available. Totalview has a good GUI with an intuitive ``dive'' feature and a coherent approach to debugging parallel programs. It is integrated with MPICH (the ch_p4, ch_shmem, and ch_lfshmem devices), understands MPI communicators and MPI message queues and ``captures'' MPI processes as they start. Totalview runs on IBM RS6000, Sun and Digital platforms. By the end of 1997 it is expected to run on SGI R10000 platforms as well.